The present invention relates to a filter for removing dissolved solids and other contaminants from water and, more particularly, to a cartridge filter having either a single solid filter through which a balanced flow is attained or dual concentric filter media through which serial radial and axial flow is controlled and balanced by a flow distribution apparatus between the two filter media.
Small cylindrical tubular filters utilizing various types of filter media useful in treating domestic water supplies are well known in the art. Activated carbon has been widely used because of its ability to absorb and filter a wide range of dissolved and suspended solids, as well as dissolved gases. To alleviate the problem of handling and retaining powdered activated carbon filter material, porous blocks of resin-bonded powdered activated carbon have been developed. In one embodiment, porous carbon filter blocks are formed in a long cylindrical shape with a hollow axial interior. Such a cylindrical filter block is placed in a suitable housing and raw water to be filtered is supplied in a manner to cause it to flow radially inwardly through the porous filter block to the hollow interior from which it is collected for use from one open end. It is also known to fill the hollow interior of the cylindrical block with another filter media in particulate form to provide supplemental filtration or water treatment.
U.S. Pat. No. 3,289,847 (Rothemund) shows a dual bed filter comprising a hollow cylindrical outer filter having its interior filled with a different type of particulate filter material. Activated carbon and an ion exchange resin are disclosed for use in two concentric filter beds. U.S. Pat. No. 4,032,457 (Matchett) discloses a tubular cylindrical filter cartridge containing activated carbon in a bonded matrix. In one embodiment, the hollow interior of the cartridge may be filled with a particulate ion exchange resin. U.S. Pat. No. 3,375,933 (Rodman) shows a cylindrical tubular filter module comprising activated carbon particles encapsulated in a polymer resin matrix. It also discloses a similar filter module comprising a powdered ion exchange resin similarly bonded with a suitable polymer. The use of a mixture of cation and anion exchange resins is also disclosed.
Resin-bonded powdered activated carbon filter blocks have gained widespread use in drinking water filter systems. Activated carbon is known to be effective for the removal of a wide range of dissolved and suspended solids, including metals and other dissolved minerals, colloidal and other suspended solids, dissolved gases, and even bacteria. As indicated, it is also known to combine other filter materials and media with porous activated carbon blocks to provide series filtration for materials which cannot be removed by the carbon or whose removal in a carbon filter is not particularly effective. For example, the interior of a hollow cylindrical carbon block filter may be filled with a wide variety of particulate filter media including minerals, resins or metals, in either finely divided or granular form. Mixtures of different types of filter media may also be utilized.
A porous carbon block filter formed with a hollow cylindrical body provides a relatively high filter capacity with a relatively small volume of filter material, and a corresponding low resistance to liquid flow through it. However, in order to provide optimum treatment capability and maximum life, it is most desirable that the radial flow of water or other liquid through the cylindrical outer wall be evenly distributed along its full axial length. Unfortunately, in the manner in which these filters are commonly used, with the radial flow into the hollow interior directed axially to one open outlet end, there is a tendency for the radial flow to be short circuited through the end of the body closest to the outlet. As a result, much of the axial length of the filter body may not be effectively utilized or utilized at all, the larger volume of liquid flow concentrated in a small filter area may not be adequately treated, and tests of the effluent from the filter may indicate failure or exhaustion of the media.
In a typical filter cartridge construction utilizing a hollow cylindrical carbon block having its open interior filled with another filter media, a similar problem concerns the difficulty in obtaining uniform radial flow through the carbon block and subsequent maximized axial or column flow through the interior media bed. For example, one commonly used filter cartridge is adapted to be installed in a housing in which both the raw water inlet and the filtered water outlet are located in the cover for the housing. In this construction, as in the application utilizing a hollow cylindrical carbon block filter alone, there is a tendency for the incoming water to short circuit and take the most direct route radially through the end of the carbon block immediately adjacent the inlet and then axially through only a short length of the media bed to the filtered water outlet. Short circuiting of the flow prevents the most effective use of the entire filter cartridge, particularly those portions at the opposite axial end remote from the inlet and/or outlet. The above identified patent to Matchett recognizes this problem in a filter cartridge of the type having an inlet in one end and the outlet in the other end. However, in order to reduce short circuiting, radial flow through a portion of the length of the outer tubular filter is substantially restricted or eliminated. The problem of short circuiting becomes more acute in certain situations, such as those applications in which the interior media bed comprises an ion exchange resin, where sufficient residence time of the water is critically important to effect the desired ion exchange. Thus, nonuniform flow distribution and short circuiting of the water not only results in inefficient use of the interior filter media bed, but may also substantially diminish the filtering or absorption capability of the carbon body.
The problem of short circuiting and lack of adequate axial distribution of the radial flow through a hollow cylindrical carbon block filter are also common to other filters having the same generally rigid self-supporting body of the same shape, but having a different type of porous filter medium. Thus, hollow cylindrical filter bodies may also be constructed of materials such as ceramics, resin bonded cellulose, bonded fibers, and a variety of other bonded particulates.